1. Field of the Invention
The present invention relates to a ventilation cover structure for an outboard engine provided with a four-stroke cycle engine and which detachably clamps to the transom of a boat to propel the boat. More particularly, the present invention relates to a ventilation cover structure for an outboard engine provided with a four-stroke cycle engine, which improves the performance of the four-stroke cycle engine by discharging hot air heated by the four-stroke cycle engine from the engine room of the outboard engine.
2. Description of the Related Art
An outboard engine has an engine disposed in an enclosed engine room to make it difficult for water to leak into the intake system of the engine and to wet the engine. Consequently, hot air is liable to stagnate in the engine room and the hot air tends to reduce the output of the engine because the hot air raises the temperature of intake air.
Hot air discharging means for effectively discharging hot air heated by heat generated by the engine outside the engine room are disclosed in JP-A Nos. Sho 59-10093 and Hei 8-100647 to solve the foregoing problem. These known hot air discharging means are intended for application to outboard engines provided with a four-stroke cycle engine, and the hot air discharging means serves also as a cover extended over the engine to cover a timing belt for driving valves and to prevent the engine from being wetted with water. Particularly, the hot air discharging means disclosed in JP-A No. Hei 8-100647 ventilates the engine room positively by using a ventilation cover to suppress the rise of the temperature of intake air. This is done by discharging not only hot air heated by the engine, but also by stagnating around the walls of the engine disposed directly below the ventilation cover outside the engine room. Each of those known hot air discharging means uses a ventilation duct formed of an upper cover extended over and covering rotating members respectively having large diameters, such as a flywheel and a crank pulley mounted on the crankshaft of the engine, and a lower cover extended under and covering the same rotating members. This ventilation duct places restrictions on an engine assembling procedure. The upper cover is a single, large structure formed of a resin and covering a wide space extending from a region around the camshaft of the engine to a region around the crankshaft of the engine. Therefore, a large mold is necessary to form the upper cover, which increases the cost of the ventilation duct.
Accordingly, it is an object of the present invention to solve the foregoing problems in the known ventilation cover structures for an outboard engine provided with a four-stroke cycle engine; and to specifically provide a ventilation cover structure for an outboard engine having a four-stroke cycle engine, which does not place any restriction on an engine assembling procedure, is formed of small component parts and capable of being formed at low manufacturing costs, and achieves a satisfactory ventilating function.
According to one aspect of the present invention, a ventilation cover structure for an outboard engine provided with a four-stroke cycle engine having an engine block, a vertical crankshaft having an upper end portion projecting upward from the engine block, a vertical camshaft having an upper end portion projecting upward from the engine block, a belt-drive transmission mechanism including a camshaft driving pulley mounted on the upper end portion of the crankshaft, a camshaft pulley mounted on the upper end portion of the camshaft, and a belt extended between the camshaft driving pulley and the camshaft pulley to interlock the crankshaft and the camshaft, and a flywheel disposed above the camshaft driving pulley and mounted on the upper end portion of the crankshaft; and engine covers defining an engine room in which the four-stroke cycle engine is disposed comprises: a first cover disposed above the engine block so as to cover at least the flywheel and opening downward; and a second cover disposed above the engine block so as to cover a space extending over a portion of the engine block on the side of the camshaft and opening downward; wherein the first and the second covers are united together so that spaces covered with the first and the second covers are united in a single space, and sections of the first and the second covers lying outside a space occupied by the flywheel jointly form a discharge duct defining a space communicating with the single space covered with the first and the second covers.
Since the ventilation cover structure in the above aspect of the present invention for covering the space over the engine block of the four-stroke cycle engine of the outboard engine in which the crankshaft and the camshaft project upward from the engine block, i.e., a vertical four-stroke cycle outboard engine, comprises the first cover covering at least the flywheel mounted on an upper end portion of the crankshaft, and the second cover covering the space extending over the portion of the engine block on the side of the camshaft, water leaked in an upper region of the engine room over the vertical four-stroke cycle engine can be prevented from falling on the belt-drive transmission mechanism and the flywheel.
Since the ventilation cover structure of the present invention does not cover the belt-drive transmission mechanism and the flywheel from below, the component parts of the belt-drive transmission mechanism and the flywheel do not need to be removed when incorporating the ventilation cover structure into the four-stroke cycle engine, and the ventilation cover structure including the first and the second covers can be very simply and easily attached to the four-stroke cycle engine provided with the belt-drive transmission mechanism and the flywheel.
Since the ventilation cover structure of the invention, capable of entirely covering a space over the four-stroke cycle engine is divided into the first and the second covers, each of which is smaller than the entire ventilation cover structure, the first and the second covers can be formed by molding using relatively small molds, which enables the manufacture of the ventilation cover structure at a comparatively low manufacturing cost.
Hot air heated by the four-stroke cycle engine and stagnating around the engine block and the belt-drive transmission mechanism can be surely collected by the first and the second covers opening downward, and is discharged through the discharge duct upward from the ventilation cover structure. Thus, the ventilation cover structure exercises a satisfactory ventilating function, which enhances the output of the four-stroke cycle engine.
Since the discharge duct is formed by overlapping portions of the first and the second covers, lying outside a space occupied by the flywheel so as to define a space communicating with the single space defined by the first and the second covers, a space extending over the engine block can be effectively used and the discharge duct has a high discharging ability.
Each of the first and the second covers may be formed by molding using a split mold that can be split along a parting face into an upper half mold and a lower half mold. Thus the first and the second covers can be produced at a high productivity and at a low cost.
Each of the first and the second covers may be formed by molding using a mold that can be split along a horizontal parting plane into an upper half mold and a lower half mold in a molding of a shape that can be easily removed from the mold. Thus, the first and the second covers can be produced at a high productivity and at a low cost.